Roadside Vegetation Management Research

WSDOT is committed to maximizing the efficiency and effectiveness of roadside maintenance and to minimizing herbicide use wherever practical. Research efforts are focused on key aspects of roadside design, construction and maintenance, in relation to the safety of the highway system, control of invasive species, and the overall sustainability of roadside plant communities and vegetation maintenance practices.

Current research projects:

Assessment of Alternatives in Vegetation Management at the Edge of Pavement

Throughout the last half of the twentieth century, over half of herbicide used annually by WSDOT was applied along the edge of pavement to maintain a vegetation-free condition in a 2 to 10 foot band along most sections of highway. Experience had shown this to be an efficient and effective way to facilitate stormwater run-off, preserve pavement life, reduce fire potential, and provide for traffic visibility. However, it was observed that several Washington Counties and a number of other State DOT’s were managing pavement edges as grass stands. In 2004, WSDOT began a long-term research project to find practical alternative practices for maintenance of vegetation at the edge of pavement and to determine the costs and results of alternative approaches.

Initial Analysis by the University of Washington (UW)
The initial analysis, led by the UW, gathered information on:

  • other research
  • other state's practices
  • maintenance costs
  • effectiveness
  • environmental effects
  • safety of traffic and maintenance operations

A full description of the proposal for the initial study is available, including the problem description, objectives, products and tasks . (pdf 19 kb)

The initial study found that there were a number of alternative approaches to managing vegetation at the edge of pavement, however there was no documentation of the long term costs and results of various practices.

Research Documents:


Field Trials




In order to further study the application of various techniques for managing vegetation at the edge of pavement a series of case studies were established in 43 sites across the state. Methods and results were documented over a period of three years to establish a comparison of average costs and long-term impacts on highway maintenance and operations.

The final report on field trials, WA-RD 736.1 was published May 2010.

For more information, contact Ray Willard at (360) 705-7865 or James Morin at (509) 577-1912.

Sustainable Roadside Design and Maintenance for Urban Freeways in Western Washington

There are unique challenges to the design, construction and maintenance of roadsides along limited access freeways in urban settings. Creating and maintaining a sustainable plant community in these situations is much more difficult than in less populated areas. This is due to combination of higher public expectations for a more park-like appearance with the increased costs of maintenance due to high traffic volumes, challenges in access, increased weed pressures, the potential for transient encampments, and the actual time and materials required to maintain a more ornamentally landscaped roadside.

Over the past 50 years, WSDOT has had mixed results in planting design and vegetation maintenance on freeway rights of way in urban settings throughout Western Washington. This research analyzes twelve case studies in urban freeway settings throughout Western Washington. Analysis considers aspects of the initial design and construction process, subsequent maintenance actions and/or projections following construction, and the resulting condition and appearance of the vegetation over time.
Due to the extreme variation in urban roadside environments and required vegetative functions, the report does not recommend a single type of roadside planting or maintenance suitable for all situations. Conclusions and recommendations are given under five categories: general, agency communication and process, design, construction, and maintenance.

The final report WA-RD 774.1 was published in July 2011.

For more information, contact Ray Willard at (360) 705-7865